1. Technical Field
The invention relates generally to electronic oscillator circuits, and more specifically, circuits and methods for decreasing the start-up time of an oscillating circuit used to drive an electro-mechanical ultrasonic medical device.
2. Background of Related Art
The benefits associated with the use of ultrasonic energy powered devices, and in particular ultrasonic instruments for surgical use, are well known. For example, the use of an ultrasonic generator in conjunction with a surgical scalpel facilitates faster and easier cutting of organic tissue while accelerating coagulation. Improved cutting results from increased body tissue to scalpel contact caused by the high frequency of vibration of the scalpel blade with respect to body tissue. Improved coagulation results from heat generated by contact between the scalpel blade and the body tissue as the scalpel blade is vibrated at a high frequency.
Conventional ultrasonic instruments include a variety of probes (e.g., cutting blades, shears, hook, ball, etc.) adapted for specific medical procedures. The ultrasonic probe is disposed at a distal end, the end furthest away from the surgeon, of the ultrasonic instrument. These ultrasonic instruments are primarily used in a variety of medical procedures including open surgical procedures, luminal procedures and endoscopic procedures.
Ultrasonic instruments are typically intermittently energized by a clinician to create the desired surgical effect (e.g., cutting, bonding, coagulation, etc.). Ideally, the ultrasonic instrument provides an instantaneous response or zero delay time between the time when the clinician energizes the instrument and the time when the surgical effect is delivered. Unfortunately, unlike electro-surgical instruments such as an RF or microwave powered instrument, an ultrasonic instrument is an electro-mechanical system that requires a start-up period during which the mechanical portion of the end effector begins to resonate at the proper oscillation frequency.
The present disclosure provides alternative methods of initiating the start-up of an oscillation circuit. Alternative methods of providing impetus injection for initiating a start-up are also disclosed that may be employed independent of the oscillation feedback type (e.g., positive or negative feedback oscillators, adaptive or fixed frequency oscillators, or self-oscillating PLL based systems).